December 03, 2012
On the Achievable Bit Rates of DSL Vectoring Techniques in the Presence of Alien Crosstalkers
Using extensive computer simulations, achievable bit rates of several vectoring techniques for digital subscriber line (DSL) systems are investigated in presence of alien crosstalkers assuming beta distribution for crosstalk couplings. Vectoring in conventional as well as phantom mode (PM) VDSL2 transmission have been considered. Vectoring techniques at the access-node (AN), such as the zero-forcing equalizer (ZFE), ZF generalized decision feedback equalizer (ZF-GDFE), linear minimum mean squared error (MMSE), and MMSE-GDFE, have been studied in US direction and zero-forcing precoder (ZFP) has been studied in DS direction. Vectoring has also been considered at the customer premises (CP) in PM transmission. The results show that when there are no alien crosstalkers, the simple ZFE is enough to reach crosstalk-free rates in US direction. However using a MMSEGDFE, considerably higher bit rates can be achieved for long loops in presence of alien crosstalkers. In DS direction, ZFP could achieve crosstalk-free rates in absence of alien crosstalkers. The results also show that use of vectoring techniques at the CP in PM transmission does not increase the achievable bit rates in US or DS directions when vectoring is already employed at the AN. Index Terms--Digital subscriber line (DSL), minimum mean squared error (MMSE) equalizer, MMSE generalized decision feedback equalizer (GDFE), VDSL2, vectoring, Zero-forcing equalizer (ZFE), ZF-GDFE, ZF precoder (ZFP).